in reply to Weird substitution, missing output

Suppose you have a program consisting of just >. What happens to it when you run your code:

  1. s/>/\t\t++k;\n/g; transforms it into \t\t++k;\n
  2. s/</\t\t--k;\n/g; does nothing, it's still \t\t++k;\n
  3. s/\+/\t\t++*k;\n/g; transforms each + present in the program into \t\t++*k;\n, leaving you with \t\t\t\t++*k;\n\t\t++*k;\nk;\n
One way to solve it would be to create a hash of all possible replacements: 
my %sub = {
 ">" => "\t\t++k;\n",
 "+" => "\t\t++*k;\n",
 ... # fill as needed
}

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Then run the substitution only once, on each symbol: 
s/(.)/$sub{$1}/ge

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Fixing the warnings about undefined hash elements (when do they happen?) and/or constructing a regular expression that would only match brainf*ck characters is left as an exercise for the reader.

A faster, but less elegant solution would be to replace + and - first, then consider other characters which might produce their own [+-].

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Re^2: Weird substitution, missing output
by AnomalousMonk (Archbishop) on May 10, 2019 at 18:25 UTC 
    my %sub = {
 ">" => "\t\t++k;\n",
 "+" => "\t\t++*k;\n",
 ... # fill as needed
 }

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    The hash initialization statement above should use parentheses and not curlies:
        my %sub = ( ... );

    s/(.)/$sub{$1}/ge

    Also note that the  /e modifier is not needed in this substitution (although it does no harm except to burn some time) because  $sub{$1} is already a scalar that can be interpolated into a string.

    Give a man a fish:  <%-{-{-{-<

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[d/l]
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      Thanks for the corrections. I should have noted that my reply was prepared on a mobile device and mostly untested.
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Re^2: Weird substitution, missing output
by timpoiko (Acolyte) on May 10, 2019 at 12:13 UTC
    Thank you. Because this is a rough translator, I fixed this using non elegant method. 
            s/</\t\tAAk;\n/g;
        s/>/\t\tBBk;\n/g;
        s/\+/\t\tAA*k;\n/g;
        s/\-/\t\tBB*k;\n/g;
        s/\./\t\tputchar(*k);\n/g;
        s/\,/\t\t*k = getchar();\n/g;
        s/\[/\twhile (*k) {\n/g;
        s/\]/\t}\n/g;
        s/A/+/g;
        s/B/-/g;

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[d/l]
      You seem to also want indentation with "\t", which means you need to keep count of the loop levels.

      Here a much easier to maintain code, looping over a split and keeping track of indentation.

      And you can easily adapt this code to emit other languages - like Perl° - too, without worrying about polluted input.

      use strict;
use warnings;
#use Data::Dump qw/pp dd/;
#use feature qw/say/;

my @table = split /\n/, <<'__TABLE__';
>    ++k;
<    --k;
+    ++*k;
-    --*k;
.    putchar(*k);
,    *k = getchar();
[    while (*k) {
]    }
__TABLE__

my %trans = map { split/\s+/, $_, 2 } @table;
#pp \%trans;



my $bfs   = '+[--[--]->+++<]>+.---';
my $level = 0;

for my $atom ( split //, $bfs ) {

    $level-- if $atom eq "]";
    print "\t" x $level;
    $level++ if $atom eq "[";
    
    print $trans{$atom};
    #print "\t\t\t// was '$atom'";         # debug
    print "\n";
}

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      ++*k;
while (*k) {
    --*k;
    --*k;
    while (*k) {
        --*k;
        --*k;
    }
    --*k;
    ++k;
    ++*k;
    ++*k;
    ++*k;
    --k;
}
++k;
++*k;
putchar(*k);
--*k;
--*k;
--*k;

      [download]

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

      update

      °) which would allow you to use the perldebugger to step thru BF code.

      update

      changed code to improve readability

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